The main RF interference sources in the Dual-mode Terminals and the required C/N for CDMA receiver operating normally are discussed first considering government regulatory requirements. Secondly, The C/N received at CDMA receiver input under the cases of Co-channel and adjacent channel interference generated by GSM transmission are calculated respectively. Finally, the solution for suppressing the interference of GSM transmission to CDMA is given and experiment results are shown. The result can be used for reference in the design of multimode RF products.